Driving circuit for electronic timepiece

ABSTRACT

A driving circuit for an electronic timepiece having two pairs of transistors of different conductivity. The driving circuit is coupled to a two-terminal driving coil fixed in the gap between the plates of a balance wheel, said balance wheel being provided with a magnetic circuit formed from two pairs of permanent magnets, one of said pairs being mounted on each of said plates. The pairs of transistors are rendered conductive alternately the moment a relatively large impulse is induced in the coil to apply a driving current to said coil.

UnitedStates Patent 1 Tsurui shi [111" 3,828,545 51 Aug. 13, I974 DRIVING CIRCUIT FOR ELECTRONIC TIMEPIECE [75] Inventor: Yuki Tsuruishi, Suwa, Japan [73] Assignee: Kabushiki Kaisha'Suwa Seikosha,

Tokyo, Japan [22] Filed: Apr.6,1972

[21] Appl. No.1 241,603

30 Foreign Application Priority Data Apr. 8, 1971 [52] US. Cl 58/28 A, 58/23 A, 318/133, 331/116 M [51] Int. Cl.... C04c 3/0'4, H02k 33/04, H03b 5/36 [58] Field of Search... 58/23 R, 23 A, 2-3 AC, 28 A; 3l8/l25,126, 132, 133; 331/113 R, 116 M,

v 154 [56] References Cited UNITED STATES PATENTS 3,363,410 [/1968 lmahashi 58/34 Japan 46-21369 3,407,344 10/1968 Bansho 58/28R Prirr zary Examiner-Edith Simmons Jackmon Attorney, Agent, or Firm-Blum, Moscovitz, Friedman & Kaplan 157] ABSTRACT A driving circuit for an electronic timepiece having 6 ims, p awiaa fisut 1 lllllllxlll'i PAn-mmmm w 3328.545

sum 2 BF 2 FIG.4

DRIVING CIRCUIT FOR ELECTRONIC TIMEPIECE BACKGROUND OF THE INVENTION This invention relates to driving circuits for electronic timepieces, and in particular, to driving circuits for electronic timepieces having balance wheels formed with magnetic circuits. Hitherto, most of the driving circuits for balance wheels took the form of astable blocking oscillation circuits having both a driving coil for energizing the balance wheel and a detecting coil to detect an oscillating phase of the balance wheel. Such driving and detecting coils are generally mounted coaxially and are positioned so as to interlink the magnetic field of the permanent magnets fixed to the balance wheel when the balance wheel is still. Upon the oscillation of the balance wheel, the magnetic field generates an induced voltage in the detecting coil which causes the driving circuit to apply a driving'current to the driving coil. Generally, the greater the number of turns in the driving coil, the higher the efficiency obtainable in the device. However, the number of winding turns in the driving coil is limited due to the necessity for a detecting coil.

One proposed solution of this problem is the provision of a single coil circuit, wherein said single coil serves as both a detecting coil and a driving coil. However, in the well known driving circuits, the balance wheel must be driven once during each period of oscillation to obtain high efficiencies. Where the amplitude of the balance wheel is limited so that it lies within 180, and if two magnetic circuits are provided on the balance wheel spaced by 180 from each other, then an astable multivibrator circuit vprovidedwith two driving SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, an electronic timepiece is provided including a balance wheel having upper and lower plates and two pairs of permanentmagnet pieces positioned to define a magnetic circuit with one of the pairs of permanent magnets being mounted on each of said plates. A twoterminal coil is fixed in the gap between said plates so as to interlink with the magnetic field of said magnetic circuit when said balance wheel is still. A driving circuit is provided including a battery and said coil for switching the driving current flowing in the coil in response to the motion of said balance wheel. Said driving circuit includes two pairs of transistors having different conductivity, said pairs of transistors being rendered conductive alternately the moment a relatively large impulse is induced .in the coil so that driving current is alternately applied in opposite directions to said coil in accordance with the reciprocating motion of the balance wheel.

Said driving circuit may include two PNP transistors and two NPN transistors, the emitter electrode of each PNP transistor being connected to the positive terminal of the battery and the emitter electrode of each NPN transistor being connected to the negative terminal of the battery. A collector electrode of each of the PNP transistors is, connected to the collector electrode of one of the NPN transistors so that four transistors define a bridge, said two-terminal coil and a decoupling condenser being connected in parallel between the respective connecting points of the collector electrode of the transistors. Resistors are connected between the base electrode of each PNP transistor and the connecting point of the other PNP transistor while coupling condensers are connected between the base electrode of each NPN transistor and the connecting point of the collector electrode of the other NPN transistor. Bias resistors are connected between the base electrode of each NPN transistor and the positive terminal of said battery.

Accordingly, it is an object of this invention to provide a novel and improved driving circuit for a balance wheel'which has very high efficiency and consumes only small amounts of electric power.

Still other other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the followingdescription taken in connection with the accompanying drawings, in which:

-.FIG. 1A is a side elevational view of a balance wheel construction of an electronic timepiece;

FIG. l'B'is a top plan view of the balance wheel construction of FIG. 1;

FIG. 2 is a waveform diagram of the induced voltage in aconventional detecting and driving coil arrangement;

FIG. 3 is a prior art driving circuit for a balance wheel; 7

FIG. 4 is a driving circuit for a balance wheel in accordance with the invention;

FIG. 5 shows the waveform of the induced voltage in the coil of the driving circuit of- FIG. 4; and

FIG. 6 is an alternate embodiment of a driving circuit for a balance wheel in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS -Referring now to FIGS. 1A and 1B, the balance wheel construction depicted therein consists of a balance wheel 1 consisting of a pair of spaced plates mounted on a balance staff 3, said balance staff being coupled to a hairspring 2 shown sectioned. A pair of permanent magnets 40, b are mounted on the undersurface of the upper plate of balance wheel I, while a second pair of permanent magnets 5a, b are mounted on the upper surface of the bottom plate of said balance wheel. The four permanent magnets define a magnetic circuit and are of a polarity such that a magnetic flux flows in the space therebetween and closes a loop. Balance weights 6 are provided spaced from the permanent magnets to balance the balance wheel. A twoterminal coil 7 is supported in the space between the permanent magnets 4a, b and 5a, b by a coil support 8.

The waveforms of the voltage induced in coil 7 by the I motion of balance wheel 1 is depicted in FIG. 2. A conventional driving circuit for a balance wheel arrangement is depicted in FIG. 3. Battery 9 is connected in series witha driving coil 11, a resistor 14, and the emitter-collector path of transistor 16. A detecting coil 10 is connected in series with capacitor 12 in the base circuit of said transistor. Resistor 13 is provided as a bias resistor for the base of transistor 16 while decoupling condenser is provided for preventing harmonic oscillation of the driving circuit. Resistor 14 is preferably adjustable for providing means for adjusting the amplitude of oscillation of the balance wheel.

When the balance wheel is vibrating, the voltage 17 (FIG. 2) is induced in detecting coil 10. As the driving coil is wound in the reverse direction to detecting coil 10, the induced voltage in the driving coil 11 is shown by line 18 in FIG. 2. When the induced voltage 17 in the detecting coil 10 is positive, the driving transistor value.

16 is rendered conductive and the collector voltage of the transistor 16 drops. Accordingly, a current as shown by area 19 in FIG. 2 flows in the driving coil 11. Since the bias level of the base electrode of the driving transistor 16 can be adjusted by a time constant determined by the product of the capacitance of condenser 12 and the resistance of bias resistor 13, the double pulse 20 can be produced or restrained. However, as

- the induced voltage 18 in the driving coil 11 is small where double pulse 20 is produced, the driving current and the joule-loss of the driving coil 11 and the resistor 14 become large, and driving efficiency is low. In order to keep efficiency high, it is necessary to drive the balance wheel only by the single pulse 19. However, in this arrangement, the balance wheel is driven once each period, so that sufficient amplitude in the oscillation of the vibration of the balance wheel cannot be obtained, and the balance wheel is readily disturbed by external shock. I

These deficiencies are overcome by the arrangement in accordance with the invention as depicted in FIG. 4.

In said arrangement, battery 21 is connected with the positive terminal thereof coupled to the respective emitters of PNP transistors 22 and 23. The respective collectors of said PNP transistors are connected to the respective collectors of NPN transistors 33 and 30, the respective emitter electrodes of said NPN transistors being connected to the negative terminal of battery 21. Resistor 24 is connected between the base of transistor 22 and the collector of transistor 23, while resistor 25 is connected between the base of transistor 23 and the collector of transistor 22. Resistor 26 is connected between the base of transistor 30 and the positive terminal of battery 21, while bias resistor 27 is connected between the base of transistor 33 and said positive battery terminal. Two-terminal coil 28 is connected between the connection points of the respective collectors of the four transistors in parallel with a decoupling condenser 29 which serves to prevent harmonic oscillation. Coupling condenser 31 connects the base of transistor 30 to thecollector of resistor 33, while coupling condenser 32 connects the base of transistor 33 with the collector of transistor 30.

The same voltage as is shown in waveform 18 of FIG. 2 is induced in coil 28. Either transistor 30 or transistor 33 is rendered conductive in response to the positive or negative polarity of the induced voltage if transistor 33 is rendered conductive, its collective voltage drops down and a base current flows into the base electrode of PNP transistor 23 through resistor 25 and transistor 23 is rendered conductive. Consequently'a driving current flows through transistor 23, coil 28, transistor 33 and battery 21.

The voltage waveform which appears in coil 28 is depicted in FIG. 5. Depending on the time constant of the coupling condenser 31 (32') and the bias resistor 26 (27), double pulses 36, 37 can be produced or restrained. In order to secure high driving efficiency, double pulses 36 and 37 must be restrained and the balance wheel must be driven by only the single pulses 34, 35. However, in this'case, the balance wheel is driven once at each half period, sothat the amplitude of the balance wheel can be maintained at a sufficiently large Since the time constant of the condenser 31 (32) and the bias resistor 26 (27) is made several times larger .the product of the resistance of coil 28 and the direct current amplification ratio h of the PNP transistor 22 (23). The driving circuit of FIG. 4 operates as follows, When an induced voltage is generated in coil 28 due to the oscillation of the balance wheel, both of transistors 22 and 30 are rendered conductive. Thus, when transistor 30-is rendered conductive, the base current flows into the base of transistor 30v through coupling condenser 31. This base current charges coupling con denser 31, the potential stored in said'condenser serving as a bias potential applied to the base of transistor 30 in the negative direction. If the product of resistor 26 and coupling condenser 31 (the time constant) is large, the bias potential in the negative direction applied to the base of transistor 30 by the charging of coupling condenser 31 will be slowly discharged through resistor 26 after the base current is cut off. Accordbodiment of FIG. 4, but a coupling condenser and bias' resistor may be connected with the base electrode of the PNP transistors and a base resistor may be connected withthe base electrode of the NPN transistors. This arrangement is depicted in the circuit of FIG. 6, wherein like reference numerals have been applied to elements corresponding to elements of FIG. 4, except that said reference numerals are primed in FIG. 6. In the embodiment of FIG. 6, coupling condenser 31 (32') is connected with the base electrode of PNP transistor 23' (22) and to the collector of PNP transistor 22 (23'). Base resistor 24 (25) is connected between the base of NPN transistor 33'(30') and the collector of NPN transistor 30 (33'). Finally, bias resistor 26' (27)'is connected between the base of transistor 23 (22) and the negative terminal of battery 21. The circuit of FIG. 6 functions in the same manner as the circuit of FIG. 4. While the driving circuit is depicted in connection with a balance wheel, the driving circuit can also be used in connection with a mechanical vibrator, and in particular, in connection with a tuning fork.

Since, in the arrangement according to the invention, the balance wheel can be driven once at each half period by means of only a single two-terminal coil at high efficiency, a novel electronic timepiece is provided. Said timepiece is characterized by low power consumption and high precision. Further, by forming the transistors of FIG. 4 in a monolithic integrated circuit, the disadvantages of the increased number of elements can be avoided. The arrangement in accordance with the invention is particularly adapted for application to a high beat electronic watch.

It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. An electronic timepiece comprising mechanical vibrator means; magnetic circuit means mounted on said mechanical vibrator means having an air gap in the path of flow of the magnetic flux; a two-terminal coil positioned to lie in said magnetic circuit means air gap when said vibrator means is still for cooperation with said magnetic circuit means to sustain the oscillation of said mechanical vibrator; a battery having positive and negative terminals for providing energy for maintaining the oscillation of. said vibrator means; and driving circuit means including said two-terminal coil and said battery for selectively applying alternating driving current to said coil in response to relatively large impulses induced in said coil by the motion of said vibrator means to maintain the oscillation of said vibrator means, said driving circuit means including two PNP transistors; two NPN transistors; means for connecting an emitter electrode of each PNP transistor to said positive terminal of said battery, an emitter electrode of each NPN transistor to a negative terminal of said battery, a collector electrode of each PNP transistor to a collector electrode of one of said NPN transistors so that'the respective four transistors form a bridge, and said two-terminal coil between said respective collector connection points; a resistor connected between the base electrode of each of said PNP transistors and said collector connecting point of the other of said PNP transistors; a coupling condenser connected between the base electrode of each NPN transistor and the collector connecting point of the other of said NPN transistors; and a bias resistor connected between the base of each NPN transistor and the positive terminal of said battery means.

2. An electronic timepiece as recited in claim 1, wherein-said mechanical vibrator means comprises a balance wheel having upper and lower plates, said magnetic circuit means comprising two pairs of permanent magnets, one of said pairs of permanent magnets being mounted on each of said plates with said air gap there between, said permanent magnets being positioned and of a polarity to define a magnetic circuit with magnetic flux flowing in the gap therebetween between said plates.

3. An electronic timepiece as recited in claim 1, wherein the resistance of the resistor connected between the base electrode of each PNP transistor and the collector connecting point of the other of said PNP transistors is selected to be almost equal to or a little larger than the produce of the direct current amplification ratio h of said PNP transistor and the resistance of said two-terminal coil.

4. An electronic timepiece as recited in claim 2, wherein the time constant as determined by the coupling condensers and the bias resistors connected to the base of each of said NPN transistors is selected to be several times larger than the oscillating period of said balance wheel.

5. An electronic timepiece as recited in claim 1, wherein all of said PNP transistors and all of said NPN transistors are formed in a monolithic integrated circuit.

6. An electronic timepiece as recited in claim 1, wherein said driving circuit means further includes a decoupling condenser connected in parallel with said two-terminal coil. 

1. An electronic timepiece comprising mechanical vibrator means; magnetic circuit means mounted on said mechanical vibrator means having an air gap in the path of flow of the magnetic flux; a two-terminal coil positioned to lie in said magnetic circuit means air gap when said vibrator means is still for cooperation with said magnetic circuit means to sustain the oscillation of said mechanical vibrator; a battery having positive and negative terminals for providing energy for maintaining the oscillation of said vibrator means; and driving circuit means including said two-terminal coil and said battery for selectively applying alternating driving current to said coil in response to relatively large impulses induced in said coil by the motion of said vibrator means to maintain the oscillation of said vibrator means, said driving circuit means including two PNP transistors; two NPN transistors; means for connecting an emitter electrode of each PNP transistor to said positive terminal of said battery, an emitter electrode of each NPN transistor to a negative terminal of said battery, a collector electrode of each PNP transistor to a collector electrode of one of said NPN transistors so that the respective four transistors form a bridge, and said two-terminal coil between said respective collector connection points; a resistor connected between the base electrode of each of said PNP transistors and said collector connecting point of the other of said PNP transistors; a coupling condenser connected between the base electrode of each NPN transistor and the collector connecting point of the other of said NPN transistors; and a bias resistor connected between the base of each NPN transistor and the positive terminal of said battery means.
 2. An electronic timepiece as recited in claim 1, wherein said mechanical vibrator means comprises a balance wheel having upper and lower plates, said magnetic circuit means comprising two pairs of permanent magnets, one of said pairs of permanent magnets being mounted on each of said plates with said air gap therebetween, said permanent magnets being positioned and of a polarity to define a magnetic circuit with magnetic flux flowing in the gap therebetween between said plates.
 3. An electronic timepiece as recited in claim 1, wherein the resistance of the resistor connected between the base electrode of each PNP transistor and the collector connecting point of the other of said PNP transistors is selected to be almost equal to or a little larger than the produce of the direct current amplification ratio hFE of said PNP transistor and the resistance of said two-terminal coil.
 4. An electronic timepiece as recited in claim 2, wherein the time constant as determined by the coupling condensers and the bias resistors connected to the base of each of said NPN transistors is selected to be several times larger than the oscillating period of said balance wheel.
 5. An electronic timepiece as recited in claim 1, wherein all of said PNP transistors and all of said NPN transistors are formed in a monolithic integrated circuit.
 6. An electronic timepiece as recited in claim 1, wherein said driving circuit means further includes a decoupling condenser connected in parallel with said two-terminal coil. 